1. Field of the Invention
The invention relates to a planetary carrier, a planetary gear mechanism, and a vehicle differential provided with such a planetary carrier or a planetary gear mechanism. In particular, the invention relates to a planetary carrier and a planetary gear mechanism that transmit the drive torque from a drive power source to planetary gears, and a vehicle differential provided with such a planetary carrier or a planetary gear mechanism.
2. Description of the Related Art
As a conventional vehicle differential, a planetary gear differential is already available, for example (Japanese Patent Application Publication No. 2003-314663 (JP-A-2003-314663)).
The vehicle differential includes: a plurality of planetary gears; a planetary carrier as an input member that rotatably holds the plurality of planetary gears; an internal gear as a first output member that meshes with the planetary gears placed on the planetary carrier; a sun gear as a second output member that is disposed coaxially with the internal gear and meshes with the planetary gears; and a differential case that houses the sun gear, the internal gear, and the planetary carrier in which the plurality of planetary gears are held.
Each of the plurality of planetary gears is a helical gear that has two large and small gear portions of which the pitch circle diameters differ from each other, and the directions of spiral of these gear portions differ from each other.
The planetary carrier rotates receiving a torque from the differential case and transmits the torque from the planetary gears to the sun gear and the internal gear.
The internal gear rotates receiving the torque from the planetary gears at the larger pitch-circle-diameter one of the large and small gear portions and transmits the torque to the rear axle (output shaft).
The sun gear rotates receiving the torque from the planetary gears at the smaller pitch-circle-diameter one of the two large and small gear portions and transmits the torque to the front axle (output shaft).
The differential case rotates receiving the torque from the engine of the vehicle and transmits the torque to the planetary carrier.
According to the above configuration, when a torque from the engine of the vehicle is input to the differential case, the differential case rotates about the rotation axis. When the differential case rotates, the torque is transmitted to the planetary carrier and then transmitted from the planetary carrier to the internal gear and the sun gear through the planetary gears.
In this case, because the front axle and the rear axle are connected to the sun gear and the internal gear, respectively, the torque from the engine is transmitted to the front axle through the differential case, the planetary carrier, the planetary gears, and the sun gear, and at the same time, transmitted to the rear axle through the differential case, the planetary carrier, the planetary gears, and the internal gear.
In such a vehicle differential, cylindrical, gear holding portions, of which the center axes are parallel to the rotation axis of the differential case, are provided in the planetary carrier.
The gear holding portion has a first reception hole that receives the larger pitch-circle-diameter one (large diameter gear portion) of the two large and small gear portions of the planetary gear and a second reception hole that receives the smaller pitch-circle-diameter one (small diameter gear portion) of the two large and small gear portions of the planetary gear.
The first reception hole is partially open on the inner circumferential surface side (radially inner side) and the outer circumferential surface side (radially outer side) of the gear holding portion, and the dimensions of the first reception hole are set so that the inner diameter of the first reception hole is greater than the thickness of the gear holding portion.
The second reception hole is partially open on the inner circumferential surface side (radially inner side) of the gear holding portion and the dimensions of the second reception hole are set so that the inner diameter of the second reception hole is smaller than the inner diameter of the first reception hole.
Thus, the large diameter gear portion is exposed to the outside and meshes with the internal gear through the outer side one of the two inner and outer openings of the first reception hole, and on the other hand, the small diameter gear portion is exposed to the outside and meshes with the sun gear through the opening of the second reception hole.
However, according to the vehicle differential of JP-A-2003-314663, although the tooth tip surfaces of the small diameter gear portion are supported by the gear holding portion of the planetary carrier, part of the tooth tip surfaces of the large diameter gear portion are not supported, and therefore, the planetary gears are inclined due to the reaction force generated due to the mesh with the internal gear and the sun gear As a result, there has been a problem that the planetary gears contact the opening edge portions of the first reception hole and the second reception hole during use, and therefore wear of the planetary gears and/or the gear holding portions occurs.